codeCampChallenge(CCC)is a platform based on freeCodeCamp.com (FCC). FCC has been modified to host coding competitions where answers to each question is hidden from one user to another. In addition to concealing answers, CCC has leaderboards to determine the progress of participants and live chat integration to provide ongoing support for the participants.
CCC is an open source project. You could try it out as a hosted service or look into its repositories with links below.